A method of preparing highly porous metal oxide fibers is proposed and the effects of plasma treatment time were investigated. The highly porous CuO fibers with short fibrils perpendicular to fiber axis were successfully prepared by treating the PVP/CuCl(2)center dot 2H(2)O electrospun fibers with oxygen plasma under particular parameters: the applied rf power density is 0.28 W/cm(2) and the treatment time is 5 similar to 30 min. The gas sensing properties of highly porous CuO fibers were measured by depositing the fiber mat on a microhotplate. The fibers show high sensitivity and fast response/recovery towards ethanol vapor.